1. Field of the Invention
The present invention relates generally to infrared radiation detectors and, more particularly, to multi-spectral, simultaneous infrared radiation detection devices.
2. Description of Related Art
Various infrared radiation detection devices have existed in the prior art. Single-color infrared radiation detection devices typically can be constructed with relative ease to provide greater performance, design simplicity, and reliability, as compared to multi-color infrared radiation detection devices.
Multi-color or multi-spectral infrared radiation detection devices often offer significant advantages, as compared to single-color infrared radiation detection devices, for example in connection with discriminating targets and implementing surveillance systems. Although multi-color infrared radiation detection devices have existed in the prior art, designs offering simultaneous detection over the full pixel area in at least two spectral bands with adequate pixel count, such as greater than 64 by 64, and adequate resolution, such as less than 75 microns, often require architectures or processes which compromise performance or manufacturability compared to single color detectors. Such compromising architectures may consist of special electronic readout circuits to deal with detectors of different polarity or special detector architectures which require especially difficult processing to delineate detectors. Compromising processes may be ones which require harsh etching of photodiode junction perimeters or growth of epitaxial layers over irregular structured surfaces which may further contain electronically delicate junctions.
Generally, a pixel or picture element, comprises an infrared radiation detector for each color, and readout circuits are connected to the individual infrared radiation detectors of each pixel element. This readout circuit architecture can be fabricated using standard silicon integrated circuit technology available from commercial foundries and may be a part of a larger silicon integrated circuit, other parts of which may be connected to other pixels. The silicon integrated circuit operates as an amplifier and a multiplexer for the signal generated in the detectors of each pixel by infrared radiation. Conventional architectures can carry high performance penalties by forcing the readout circuits' to deal with diodes of both p-on-n and n-on-p polarities. The readout circuits for many conventional detection devices require the subtraction of large currents within a single pixel element, wherein the single pixel element comprises two infrared radiation detector diodes, each of a different color. To preserve high performance this subtraction must be nearly noiseless. In a typical application for these devices these devices, a medium wavelength infrared (MWIR) signal is obtained by subtracting the long wavelength infrared (LWIR) generated photo-current from that generated by both the MWIR and the LWIR fluxes. The magnitudes of these currents are typically 100 to 1 (LWIR to MWIR). Even a few percent cross-talk of LWIR signal in the MWIR band will likely overwhelm the MWIR signal. Additionally, the complex subtraction circuit can rob the small input cell (for processing information from the readout circuit) of needed room for integration capacitors and field effect transistors (FET's) required for significant charge handling capability. Material growth and junction delineation in conventional devices can also compromise efficiencies and performance. A multi-color infrared radiation detection device is needed which address the above problems and, in particular, provides detection sensitivity comparable to that of single-color infrared radiation detectors, simultaneous detection in all bands or colors, broadband sensitivity within each band, low electrical and optical cross talk between pixels and colors, high optical fill factor, compatibility with existing readout circuits (common diode polarity, standard bias requirements, etc.), and minor impact on processing.